The ISO MPEG-II audio standard has developed a world-wide standard audio coding algorithm, which can significantly reduce the requirements of transmission bandwidth and data storage with low distortion. With the recent advances in VLSI and ATM networking technology, the low-cost MPEG-II audio decoder in real-time system becomes more essential for multimedia applications.
The MPEG-II audio coding standard is an extension of MPEG-I. Emphasis of the new activity is on multichannel and multilingual audio and on an extension of the existing standard to lower sampling frequencies and lower bit rates. In addition, backward compatibility is a key aspect to ensure the existing two channel decoders will still be able to decode compatible stereo information from five multichannel signals. This implies the provision of compatibility matrices, using adequate inverse matrix coefficients.
The MPEG-II decoding flow chart is shown in FIG. 1. Also, within the synthesis subband filter, the inverse Modified Discrete Cosine Transform (IMDCT) V.sub.i of a sequence S.sub.k (where N.sub.i is the cosine function defined in equation (1), below), and the inverse Pseudo Quadrature Mirror Filter (IPQMF) U.sub.ij (defined as a function of IMDCT V.sub.i, where D.sub.i is a standard windowing coefficient as defined the MPEG standard ISO CO 11172-3) will be realized, as shown in FIG. 2. The IMDCT module makes the perfect reconstruction feasible as a polyphase QMF transform kernel. The IPQMF module can be further decomposed into four functions, such as: shifting, rearranging, windowing and partial summation. According to the computation power analysis for MPEG-II audio decoding in Table 1, the computation load synthesis subband filter illustrated in FIG. 2 depends to a great extent on the realization of IMDCT module, while the IPQMF also induces substantial computation and some data arrangement. Moreover, the inverse quantization (IQ) and multichannel (MC) modules although occupying little of the computational load of the whole process, present some data access and arrangement issues which make the decoding flow more uncompact.
TABLE 1 Classification Function MOPS.sup.1) IQ Degrouping 0.88 Requantization 1.44 Rescalzation 0.96 3.28 MC Dematrixing 0.576 Denormalization 1.44 2.016 Synthesis IMDCT 61.44 Subband Filter IPQMF 19.22 81.36 Total 86.656 .sup.1) MOPS: Million Operations per Second